As well known, magnetic recording apparatus is divided into those using a magnetic disk as the medium on which to record data and those using magnetic tape as such medium. Because the former type of recording apparatus using a magnetic disk (hereinafter referred to as magnetic disk drives) is prevailing, the following description focuses on magnetic disk drives as an example of the magnetic recording apparatus.
As the capacity enlargement of magnetic disk drives has been pursued for recent years, the fly height of the magnetic head has been lowered rapidly down to below 10 nm or even less, and, consequently, there is increasing need for reliability in terms of resistance to sliding friction.
Also, there is strong need to enhance the data processing speed with more disk capacity. In particular, in a Redundant Array of Independent Disks (RAID) system, a magnetic disk drive that operates at a disk revolving speed of 10,000 rpm or higher is required.
In order to ensure the reliability of a magnetic disk drive, generally, a lubricant layer is formed on a carbon overcoat on the surface of a magnetic disk for use in the disk drive. As the main material of the lubricant layer, usually, fluoropolyether which is a chemically stable fluorinated organic compound is widely used.
Actually, in order to assure reliability of the magnetic disk drive, it is mandatory to efficiently preserve suitable lubricant distribution on the surface of said magnetic disk drive for long operating times. When magnetic disk drives operate, said disk revolve at a high speed and the lubricant might be spun off by the combined action of the air shear due to the air flow on the surface of the disk as the disk revolves, and of the centrifugal force directly exerted on the lubricant. As a consequence, it is often observed that the quantity of the lubricant on the surface of the disk gradually decreases. Also, evaporation phenomena of the lubricant into the atmosphere inside the magnetic drive may take place.
To overcome this problem of the lubricant loss by being spun off during disk revolution and natural evaporation, approaches have heretofore been proposed. Thus, a method for restraining the lubricant from being spun off and evaporated has been proposed in which the adhesion force of the lubricant to the disk protecting layer is made stronger by increasing the polarity of the functional end groups in the lubricant. Said polar end groups are believed to both improve adherence of the lubricant to the surface of the magnetic media and decrease volatility.
Within this approach, fluoropolyether lubricants based on fluoropolyethers having polar functional groups both in the end groups and in the chain have shown best performances.
Thus, JP 2006070173 (FUJITSU LTD) 16 Mar. 2006 discloses a lubricant for magnetic recording media (MRM) having fluorinated polyether structure, said lubricant comprising from 1 to 10 hydroxyl group per molecule and comprising the following structural units bound with each other through an ether bond:—CF2CH2OH (terminal group)  (1)—CF2— (inner group)  (2)—CF2CF2— (inner group)  (3)—CF2CH2O—CH2—CH(OH)—CH2—OCH2CF2— (inner group).  (4)
Similarly, US 2007060487 (HITACHI GLOBAL STORAGE TECH) 15 Mar. 2007 discloses a MRM lubricant with non-terminal functional groups; the location of the functional groups is selected so as to minimize chain length of free backbone PFPE chain between functional groups while simultaneously maximizing evaporation temperature and ensuring efficient bonding to the lubricated surface.
Further, US 2009023017 (HOYA CORP [JP]) 22 Jan. 2009 discloses lubrication of MRM surfaces by means of compounds comprising a central phosphazene ring, said central moiety being substituted with one or more perfluoropolyether chains comprising hydroxyl groups bonded thereto, so as to finally provide a number of hydroxyl group in the compounds exceeding 2.
Further, in addition, for achieving large mass-storage capacity, thanks to the merger of optical and magnetic recording technology, heat assisted magnetic recording disks have captured increasing attention; according to this technique, the magnetic recording disk made of magnetic material having large magnetic anisotropy energy (and thus not ‘writable’ as such’) is locally heated by irradiation so as to locally decrease magnetic coercive force and thus making it possible to record information via a magnetic head. Requirements for a lubricant for magnetic recording media suitable for this technique are thus even more stringent as the lubricated face of the disk is exposed, in addition to the ultra-low-height flying of the head and the extremely rapid revolution speed, to temperatures which can locally reach temperatures of 200° C. or higher. Decomposition and/or evaporation phenomena might be accelerated.
Within this context, traditional perfluoropolyether lubricants as above detailed have been found to undergo significant thermo-oxidative degradation phenomena, making thus them possibly unsuitable for being used in such heat assisted magnetic recording techniques.
On the other side, triazine derivatives comprising fluorinated moieties are known in the art.
For instance, EP 1033368 A (AUSIMONT SPA) 6 Sep. 2000 discloses fluorinated triazinic compounds of either of formulae:
wherein Z=T-Y, with T=-(CH2)q—, —SO2—, —CO—, q=is an integer from 1 to 20; Y═O—, O(C2H4O)p—, O(CH2)n—NR—, O(CH2)n—O—, O(C3H6O)p—, NR—, S—, S(C2H4O)p—, S(C3H6O)p—; wherein R═H, alkyl from 1 to 10 C atoms; n is an integer from 1 to 20; p is an integer from 1 to 5; Rf represents a linear or branched fluoroalkyl chain or a (per)fluoropolyether chain, X is selected from: Cl; Rf—CF2—Z; CF3—Z, which are taught as suitable for the manufacture of formulations for the treatment of natural or synthetic fibres textiles.
EP 1712580 A (SOLVAY SOLEXIS SPA) 18 Oct. 2006 discloses compounds of formula:
wherein, inter alia, at least one of Q1 and Q2 is a phenyl ring and T2 is either a group of formula:
in which Q1 and Q2 are as defined above, or a neutral group, possibly halogenated.
U.S. Pat. No. 6,156,937 (AUSIMONT SPA) 5 Dec. 2000 discloses, inter alia, triazine compounds of formula:
in which Rf is ClC3F6O(C3F6O)1.27(CF2O)0.05—CF2O—.
U.S. Pat. No. 5,942,598 (NIPPON MEKTRON LIMITED) 24 Aug. 1999 relates to an oily composition containing about 80 to about 95 parts by weight of a perfluoropolyether having a definite viscosity value and about 20 to about 5 parts by weight of a perfluoroalkylene triazine oligomer in which non functional perfluoropolyether chains are linked to the triazine rings.
Also, EP 1978077 A (FUJIFILM CORP) 8 Oct. 2008 discloses, inter alia, certain triazine derivatives comprising fluorinated chains interrupted by ethereal oxygens, bond to the triazine moiety through a suitable spacer, which can be used, notably, as lubricants e.g. for magnetic material films such as those of diamond-like carbon.
There is thus still a current shortfall in the art for lubricant compounds endowed with improved thermo-oxidative stability, coupled with high cohesion with support layers to be lubricated and outstanding lubricating behaviour, which would satisfy more and more demanding requirements for new MRM technologies, including heat assisted magnetic recording techniques.